Dry etching gas

ABSTRACT

Disclosed is fluorocarbon-based dry etching gas which is free of global environmental problems and a dry etching method using a plasma gas obtained therefrom. The dry etching gas includes a fluorinated ether of carbon, fluorine, hydrogen and oxygen and having 2-6 carbon atoms.

TECHNICAL FIELD

This invention relates to a dry etching gas and a plasma processingmethod for a material to be processed using the gas.

BACKGROUND ART

A dry etching technique, which is capable of forming fine patterns inthe production of IC, is utilized for the production of super LSI, etc.in lieu of wet etching.

For dry etching a semiconductor material such as silicon dioxide(hereinafter also referred to as SiO₂), a mixed CF₄ and H₂ gas, CHF₃,C₂F₆, C₃F₈, C₄F₈ or a mixture thereof is used as an etching gas for thepurpose of sufficiently increasing an etching rate ratio of the SiO₂ tosilicon (hereinafter also referred to as Si) or polysilicon (hereinafteralso referred to as polySi) on which the SiO₂ is formed. The abovefluorine-containing gases, such as CF₄, CHF₃, C₂F₆ and C₃F₈, however,have a long life in atmosphere and a large global warming potential.Namely, when discharged to air, these gases retain without beingdecomposed for a long period of time and contribute to warming of earthas a greenhouse effect gas (hereinafter referred to as GHG).

The global warming is the most important problem among various currentlyalarmed global environmental problems. Climatic Change Framework Treatyhas been adopted 1992 for the prevention of global warming. Detailedmethods of restricting GHG and schedule therefor are now discussed inmeetings of contracting states of the Treaty.

To cope with the global warming problem, various methods for reducingGHG are investigated with the simultaneous development of varioustechniques for substitutes for GHG.

Up to now, however, no effective substitutes have been found forconventional etching gas for semiconductors. Thus, the current trend istoward the decomposition of exhaust gases discharged after etching stepsso as to reduce the emission of GHG to air.

It is an object of the present invention to provide a dry etching gaswhich is free of global environment problems such as global warming anda plasma processing method for a material to be processed using the dryetching gas.

DISCLOSURE OF THE INVENTION

The present inventors have made an earnest study for solving theabove-described problem and, as a result, have found that the problemcan be solved by using an organic compound constituted of carbon,fluorine, hydrogen and oxygen and having 2-6 carbon atoms and thuscompleted the present invention.

Namely, according to the present invention, there is provided a dryetching gas comprising an organic compound constituted of carbon,fluorine, hydrogen and oxygen and having 2-6 carbon atoms.

The present invention also provides a plasma processing method for amaterial to be processed, characterized in that the material isprocessed with a plasma gas obtained from the above-described dryetching gas.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of one embodiment of a dry etchingdevice used for the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The dry etching gas used in the present invention comprises an organiccompound constituted of carbon, fluorine, hydrogen and oxygen and having2-6 carbon atoms. The organic compound has a boiling point of not higherthan 80° C., preferably not higher than 20° C.

The organic compound is preferably a hydrofluoroether. The presentinventors have investigated a relationship between the atomiccomposition of the hydrofluoroether and the etching effect and havefound that excellent etching effect is obtained by using thehydrofluoroether which satisfies with the following formula (1):

[C]/([F]+[O]−[H])<0.8.  (1)

The value R of [C]/([F]+[O]−[H]) is preferably in the range of 0.7-0.4,more preferably 0.6-0.4. When the value R is 0.8 or more, the amount ofa fluorocarbon polymer film depositing on a surface of a material to beprocessed increases during etching so that the efficiency of etching ofthe material to be processed is adversely affected.

Illustrative of suitable hydrofluoroethers are CHF₂OCF₃ (R=0.4),CF₃CHFOCF₃ ( R=0.43) and CHF₂CF₂OCF₂CF₃ (R=0.44).

The dry etching gas according to the present invention is converted intoa plasma gas for use in processing a material to be processed.

FIG. 1 is a schematic illustration of a dry etching device used in thepresent invention.

In FIG. 1, designated as 1 is a vacuum vessel, as 2 and 3 are a pair offlat plate electrodes, and as 4 is a material to be etched.

In dry etching the material to be processed using the dry etchingdevice, the dry etching gas is introduced through a conduit 6 into thevacuum vessel 1 maintained in vacuum. A high frequency voltage isimpressed between the electrodes 2 and 3 to form a plasma between theopposing electrodes 2 and 3, so that the introduced gas is decomposedand excited, thereby etching the material to be processed 4.

The dry etching gas according to the present invention may be used forvarious materials to be processed and is particularly advantageouslyused for semiconductor materials. As the semiconductor materials, theremay be mentioned silicon dioxide, especially a silicon dioxide filmformed on a surface of a silicon film or a polysilicon film.

The dry etching gas according to the present invention has an extremelyshort life when dispersed in air and, hence, scarcely causes a problemof global warming.

Life time in air and global warming factors of variousfluorine-containing gases are shown in Table 1.

As will be appreciated from Table 1, the dry etching gases according tothe present invention have an extremely short life in air and haveimproved effect of preventing global warming as compared with theconventional fluorine-containing etching gases.

TABLE 1 Global Warming Chemical Life in Air Factor Formula C/F + O − H(year) HGWP CF₄ 0.25 50,000 7.1 CHF₃ 0.50 264 7.0 C₂F₆ 0.33 10,000 10.0C₃F₈ 0.38 2,600 7.2 C₄F₈ 0.50 3,200 9.1 CHF₂OCHF₂ 0.67 19 0.61CF₃CHFOCF₃ 0.43 11 0.22 CH₃OCF₂CF₃ 1.0 1.2 0.024 CHF₂CF₂OCF₂CF₃ 0.44 6.80.13 CH₃OCF₂CF₂CF₃ 0.80 1.3 0.019

Remarks: Global warming parameter (HGWP):

value relative to CFC-11 whose global warming parameter is assigned tobe 1.0.

EXAMPLES

The present invention will be further described in detail by examples.

Example 1

The etching device used for carrying out the present invention is asschematically illustrated in FIG. 1. A material to be etch-processed 4was placed on a lower electrode 2 of a pair of opposing flat plateelectrodes 2 and 3 disposed in a vacuum vessel 1. To the vacuum vessel 1were fed an etching gas and O₂ at a total flow rate of 90 sccm and He ata flow rate of 10 sccm through a gas feed conduit 6, while maintainingthe pressure within the vessel 1 at 60 mTorr. Then, a high frequencyvoltage (frequency: 400 KHz, Power: 600 W) was impressed to theelectrodes from a high frequency electric power source 7 to generate aplasma between the opposing electrodes 2 and 3. Thus, the introduced gaswas decomposed and excited so that the material to be processed 4 wasetched. The following four kinds of gases were used for etching: HFE-134(CHF₂OCHF₂), HFE-245 (CH₃OCF₂CF₃), HFE-329 (CHF₂CF₂OCF₂CF₃) and HFE-347(CH₃OCF₂CF₂CF₃) . The results of measurement of SiO₂ etching rate in thefour kinds of HFE are shown in Table 2. The etching rate is an amount ofSiO₂ removed from the surface of the SiO₂ per 1 minute and is expressedin terms of a thickness (A) thereof.

TABLE 2 Etching Rate (Å/minute) Kind of O₂ Concentration (%) Gas 0 10 3050 HFE-134 1413 1512 1028 — HFE-245 x —  723 602 HFE-329 3148 — 1107 —HFE-347 x x x x Remarks 1: O₂ Concentration (vol %) = [O₂/(HFE + O₂)] ×100 Remarks 2: “x” indicates that it was impossible to measure becauseof deposition of a polymerized material on the wafer Remarks 3: “—”indicates that no measurement was performed

Example 2

A test was performed using HFE-329 (CHF₂CF₂OCF₂CF₃) under the sameconditions (O₂ concentration: 0%) as those in Example 1 and using thesame etching device as used in Example 1. In this test, a selectivity toPoly-Si and a selectivity to a photoresist were also measured inaddition to an etching rate Of SiO₂.

The SiO₂ etching rate was found to be 3017 Å/minute. In this case, theselectivity to Poly-Si was 16.5 and the selectivity to the photoresistwas 12.2. Thus, the SiO₂ etching rate and the selectivity werecomparable to or superior to those attained by using the conventionaletching gas. For the purpose of investigating an effect of addition ofO₂, the amount of O₂was increased from the above 0% to 10% and 20% whilemaintaining the total flow rate of HFE-329 plus O₂ at 90 sccm. As aresult, in the case of the amount of O₂ of 10%, the SO₂ etching rate was3176 Å/minute, the selectivity to Poly-Si was 1.7 and the selectivity tothe photoresist was 1.3. Thus, addition of O₂ was not found to beeffective.

The term “selectivity to Poly-Si” above is intended to refer to a ratioof the SiO₂ etching rate to the Poly-Si etching rate and the term“selectivity to the photoresist” is a ratio of the SiO₂ etching rate tothe photoresist etching rate.

Example 3

Etching was performed using HFE-227 (CF₃CHFOCF₃) under the sameconditions as tho se in Example 1 and using the same etching device asused in Example 1. In the case of the amount of O₂of 0%, the SiO₂etching rate was 3632 Å/minute, the selectivity to Poly-Si was 16.9 andthe selectivity to the photoresist was 11.1. In the case of the amountof O₂ of 20%, the SiO₂ etching rate was 2147 Å/minute, the selectivityto Poly-Si was 1.5 and the selectivity to the photoresist was 1.2.

Similar to in Example 2, even with HFE-227 by itself, satisfactory SiO₂etching rate and selectivity were obtained. The addition of O₂ was notfound to be effective.

The dry etching gas according to the present invention shows etchingeffects comparable to or superior to the customarily employedfluorine-containing gas and, moreover, does not cause problems ofserious global environmental problems such as global warming.

What is claimed is:
 1. A method for dry etching a silicon dioxide film,said method comprising: forming a plasma of CF₃CHFOCF₃ orCHF₂CF₂OCF₂CF₃; and contacting the silicon dioxide film with the plasmato dry etch the silicon dioxide film.
 2. A dry etching method accordingto claim 1, wherein said silicon dioxide film is formed on a surface ofa silicon or polysilicon film.